In aircraft gas turbines compressors are used to compress the air entering the gas turbine. For maximum efficiency the airflow entering the upstream end of the compressor must have a precise axial orientation with this orientation determined by the pitch of inlet guide vanes directing the air to the first rotor stages. Since variable operating conditions are encountered it is known to use variable inlet guide vanes which may be rotated around an axis varying the pitch to optimize the particular operating condition.
Under certain flight conditions ice can form on the inlet vanes. When this ice later flakes off, it leads to engine damage. Accordingly, it is known to supply heated air to these vanes when potential icing conditions are encountered so as to avoid ice formation on the vanes. Heated air from a high pressure compressor stage is supplied to the vanes for this purpose. Conventionally, this air will enter through the trunnion supporting the variable vane.
The trunnion is normally limited to the width of the blade particularly where it must be installed close to a support strut. Such limited size of trunnion limits the flow area available for introducing air into the guide vane. Since the vanes must be rotated through a linkage, additional complications are introduced in combining this operating linkage with an airflow to the central portion of each of the guide vanes.
Some of the guide vanes are located directly behind support struts. It is important for optimum operation that they be located in such a way that a smooth airflow transition occurs between the struts and guide vanes at all operationing conditions.